Endothelin is a 21-amino acid peptide produced by endothelial cells. The peptide is secreted not only by endothelial cells but also by tracheal epithelial cells or from kidney cells. Endothelin (ET-1) has a potent vasoconstrictor effect. The vasoconstricting effect is caused by the binding of endothelin to its receptor on the vascular smooth muscle cells..sup.1-3
Endothelin-1 (ET-1) is one of three recently identified potent vasoconstricting peptides which also includes endothelin-2 (ET-2) and endothelin-3 (ET-3) whose sequences differ from ET-1 by two and six amino acids, respectively..sup.4
Increased levels of endothelin are found in the blood of patients with essential hypertension, acute myocardial infarction, pulmonary hypertension, Raynaud's disease or atherosclerosis or in the washing fluids of the respiratory tract of patients with asthma compared to normal levels..sup.5-8
An experimental model of cerebral vasospasm and a second model of acute renal failure have led to the conclusion that endothelin is one of the mediators causing cerebral vasospasm following a subarachnoid hemorrhage, and renal failure..sup.9-10
Endothelin was also found to control the release of many physiological substances such as renin, atrial natriuretic peptide, endothelium-derived relaxing factor (EDRF), thromboxane A.sub.2,.sup.14, prostacyclin, norepinephrine, angiotensin II and substance P..sup.11-16 Further, endothelin causes contraction of the smooth muscle of the gastrointestinal tract and the uterine smooth muscle..sup.17-19 Endothelin has also been shown to promote the growth of rat vascular smooth muscle cells which would suggest a possible relevance to arterial hypertrophy..sup.20
Endothelin receptors are present in high concentration in the peripheral tissues and also in the central nervous system, and cerebral administration of endothelin has been shown to induce behavioral changes in animals, suggesting that endothelin may play an important role in controlling neural functions..sup.21
Endotoxin has been shown to promote the release of endothelin. This finding has suggested that endothelin is an important mediator for endotoxin-induced diseases..sup.22-23
A study has shown that cyclosporin added to a renal cell culture, increased endothelin secretion..sup.24 Another study has shown that administration of cyclosporin to rats, led to a decrease in the glomerular filtration rate and an increase in the blood pressure, in association with a remarkable increase in the circulating endothelin level. This cyclosporin-induced renal failure can be suppressed by the administration of anti-endothelin antibody..sup.25 These studies suggest that endothelin is significantly involved in the pathogenesis of cyclosporin-induced renal disease.
A recent study in patients with congestive heart failure demonstrated a good correlation between the elevated levels of endothelin in the plasma and the severity of the disease..sup.26
Endothelin is an endogenous substance which directly or indirectly (through the controlled release of various other endogenous substances) induces sustained contraction of vascular or non-vascular smooth muscles. Its excess production or excess secretion is believed to be one of the factors responsible for hypertension, pulmonary hypertension, Raynaud's disease, bronchial asthma, acute renal failure, myocardial infarction, angina pectoris, arteriosclerosis, cerebral vasospasm and cerebral infarction. See A. M. Doherty, Endothelin: A New Challenge, J. Med. Chem., 35, 1493-1508 (1992).
Substances which specifically inhibit the binding of endothelin to its receptor are believed to block the physiological effects of endothelin and are useful in treating patients with endothelin related disorders.
The novel compounds of the present invention are useful as a non-peptidic endothelin antagonists, and have not been disclosed in any issued patents or published patent applications. Among the published patent applications disclosing linear and cyclic peptidic compounds as endothelin antagonists are the following: Fujisawa in European Patent Application EP-457,195 and Patent Cooperation Treaty (PCT) International Application No. WO 93/10144, Banyu in EP-436,189 and 460,679, Immunopharmaceutics Inc. in WO 93/225580, Warner Lambert Co. WO 92/20706 and Takeda Chemical Ind. in EP-528,312, EP-543,425, EP-547,317 and WO 91/13089.
Fujisawa has also disclosed two nonpeptidic endothelin antagonist compounds: anthraquinone derivatives produced by a fermentation process using Streptomyces sp. No. 89009 in EP-405,421 and U.S. Pat. No. 5,187,195; and a 4-phenoxyphenol derivative produced by a fermentation process using Penicillium citreonigrum F-12880 in a UK Patent Application GB 2259450. Shionogi and Co. has also disclosed nonpeptidic endothelin antagonist triterpene compounds which were produced by a fermentation process using Myrica cerifera in WO 92/12991.
Among the nonopeptidic endothelin antagonist compounds which are known in the patent literature are: 1) a series of substituted (1,4-quinolinoxy)methylbiphenylcarboxylic acids disclosed by Roussel-Uclaf in EP-498,723; 2) a series of of N-(4-pyrimidinyl)benzenesulfonamides with different substitution patterns from Hoffmann-La Roche published in EP-510,526, EP-526,708 and EP-601,386; 3) a series of naphthalenesulfonamides and benzenesulfonamides disclosed by E. R. Squibb & Sons in EP-558,258 and EP-569,193, respectively; 4) a series of compounds represented by 3-(3-indolylmethyl)-1,4-diaza-2,5-dioxobicyclo[4.3.0]nonane-9-carboxylic acid from ImmunoPharmaceutics Inc. in WO 93/23404; 5) a series of fused [1,2,4]thiadiazoles substituted with an iminosulfonyl substituent from Takeda Chemical Ind. has been disclosed in EP-562,599; and 6) a series of indane and indene derivatives from SmithKline Beecham Corp. disclosed in WO 93/08779; and a series of related phenylalkyl derivatives from SmithKline Beecham disclosed in WO 94/02474.